Charge mobiles with body heat

Researchers at the Fraunhofer Institute for Integrated Circuits in Erlangen, Germany, have developed new circuits that can harness electricity from body heat that would otherwise be dissipated into the air. The scientists say the advance could lead to battery-less cell phones and medical monitors that draw energy from their users.

“The idea behind it is that you can replace the batteries or at least you can enlarge the operation times of batteries,” said Peter Spies, electrical engineer and group manager at the institute.

Spies and his team improved upon semiconductors called thermoelectric generators that produce electrical energy in the face of temperature differences.

Normally, a difference of several tens of degrees is required in order to generate enough power, but the difference between the body’s surface temperature and that of its environment is only a few degrees. This produces about 250 millivolts, while electronic devices require at least one or two volts.

As part of their research, Spies and his team incorporated a component into the circuit called a charge pump. The pump temporarily stores the incoming millivolts until they reach 1.8 volts. At that threshold, an internal transistor turns on and delivers the higher voltage to a component that can transfer the electricity to a device.

Matthias Ueltzen, an application engineer at Freiburg, Germany-based Micropelt, a developer and manufacturer of thermoelectrics, said, while the “idea of generating some electric power from the heat of the body is a great idea,” there are certain difficulties, which lie in the low temperature differences between the skin and the outside air.

“Only a very small part of the thermal heat flow can be converted into electrical power, and for that reason, the technology may only work for applications that don’t require a lot of energy,” said Ueltzen.

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